The present invention relates to a device for relocating a lower jaw relative to an upper jaw, especially according to the principle of a Herbst hinge. A device of that kind described by U.S. Pat. No. 5,919,042 comprises a first sleeve having a first holder mounted on its one end and an external thread provided on its other end, a second sleeve provided with a matching internal thread so that the first sleeve can be screwed into the second sleeve over different lengths, and a rod arranged in the two sleeves for longitudinal movement and provided with a second holder on its end facing away from the first holder. The two holders are configured as eyes by means of which the device can be mounted in articulated fashion on the one hand on a molar strip in the upper jaw and, on the other hand, on a molar strip in the lower jaw. The device can follow the movements of the lower jaw, when the patient chews or opens or closes his mouth, by the rod moving back and forth in the two sleeves. When the patient bites his teeth together, the holder of the rod abuts against the second sleeve, and thereafter the lower jaw is necessarily displaced relative to the other jaw as the biting action continues. That change occurs abruptly, and considering the high forces that may be applied by the strong muscles of the jaw it may be felt as unpleasant orxe2x80x94in some casesxe2x80x94even painful and may lead to damage to the teeth and to the device as such.
Now, it is the object of the present invention to overcome these disadvantages by an improved structure of the device.
The invention achieves that object by a device having the features defined in claim 1. Advantageous further developments of the invention are the subject-matter of the sub-claims.
The device according to the invention comprises three sleeves which interact with a rod in the way of a telescope. One end of the first sleeve carries a first holder. The first sleeve and the second sleeve are screwed together, for which purpose one of the sleeves is provided with an internal thread, the other one with a matching external thread. This permits the one sleeve to be screwed into the other sleeve a longer or shorter length, so as to vary the effective length of the device. One end of the third sleeve, i e. the end facing the first holder, is mounted on the second sleeve and adapted to dampen impacts that may act in the longitudinal direction. The rod is arranged in the third sleeve for longitudinal displacement and comprises a second holder, which is mounted outside the third sleeve on that end of the rod which faces away from the first holder. A stop provided on the rod in the neighborhood of the second holder, or on the second holder, abuts directly or indirectly against that end of the third sleeve which faces away from the first holder and toward the second holder. The length of the rod is selected to ensure that in its abutting position it will extend right into the first sleeve. The two holders serve to mount the device in articulated fashion on the patient""s upper jaw and lower jaw, usually on the molars of the upper jaw and the lower jaw, and those molars may be enclosed for this purpose by molar strips carrying counter-holders that coact with the respective holder of the device.
When the patient bites his teeth together, the rod then no longer abuts against the second sleeve, but rather against the third sleeve, which dampens the impact produced by the biting action. Accordingly, the device according to the invention is much more comfortable for the patient than known devices and does not cause any pain or damage when the patient bites his teeth together, neither on the teeth nor on the device as such, which furthers the patient""s willingness to wear the device and thereby accelerates the orthodontic correction of the position of the teeth intended to be achieved by the device. That effect is further strengthened by the fact that the length of the device can be increased as the correction process progresses by turning the second sleeve relative to the first sleeve without any need to remove the device from the mouth, whereby the orthodontic treatment is further accelerated, and its cost is reduced.
Conveniently, the external thread is provided on the first sleeve, namely on that end of the first sleeve which faces away from the first holder, while the internal thread is arranged on the second sleeve, likewise on that end which faces away from the first holder. If the degree of adjustability is sufficient, the second sleeve can then stabilize the sleeve and does not have to extend into the third sleeve for damping purposes, except for its threaded portion.
Preferably, the third sleeve consists entirely or in part of an elastomeric material, especially a silicon plastic material, which on the one hand offers sufficient damping properties and, on the other hand, is especially suited for use in the bacterial and electrolytically not neutral environment of the mouth. The third sleeve may, however, also consist of a combination of a rigid portion and a dampening portion. Likewise, a corrugated tube could be used for the third sleeve. One advantage of the invention is seen in the fact that it is possible, by suitable selection of the material used and of the configuration of the third sleeve, to select at desire not only the dampening efficiency, but also the dampening characteristic. The dampening characteristic may be linear, which means that after compression the resistive force decreases linearly as the third sleeve is restored to its original length; such a characteristic can be achieved, for example, with the aid of a corrugated tube. Preferably, a progressive dampening characteristic is selected, which means that after compression the third sleeve is restored to its original length superproportionally as the compressive force is relieved.
The stop of the rod may abut directly against the end of the third sleeve when the patient bites his teeth together. Especially when the third sleeve consists of an elastomeric material, entirely or in part, it is, however, advantageous if a rigid bush, especially a metallic bush that guides the rod and against which a stop of the rod can abut is fitted in that end of the third sleeve which faces away from the first holder. The bush is preferably provided for that purpose with a collar that is in contact with the end face of the third sleeve that faces away from the first holder. Such a bush may be fixed in the third sleeve by pressing, bonding or in any other way. The bush may serve not only as a stop for transmitting the forces produced during the biting action to the dampening elastomeric sleeve, but at the same as a means for guiding the rod in the longitudinal direction so that the rod is guided not only in the first and the second, but also in the third sleeve. In order to further improve the guiding effect, the third sleeve preferably contains a central portion whose inner diameter is smaller than the inner diameter of the end portion of the third sleeve by an amount which guarantees that the rod can be guided in the longitudinal direction also in the central portion of the third sleeve, in the area between the bush and the end portion of the third sleeve connected with the second sleeve. The rod then simultaneously stabilizes the elastomeric sleeve when the latter is compressed by the biting action. The rigid, preferably metallic elements of the device, namely the first sleeve, the second sleeve, the rod and the bush then coact with the dampening, especially elastomeric sleeve in a meaningful way so that on the one hand stable relocation of the lower jaw relative to the upper jaw is achieved while on the other hand the forces that occur abruptly when the patient bites his teeth together are dampened to a comfortable and well-tolerated degree.
In the third portion of the third sleeve, and in the third sleeve, the rod is guided preferably with somewhat greater play than in the bush of the third sleeve, whereby an optimum of reliable guidance on the one hand and easy movement on the other hand is achieved.
In order to permit the length of the device to be adjusted in the mouth, without any need to remove it from the mouth, the second sleeve is preferably provided with means in which a wrench can be positively engaged for turning the second sleeve. These means may consist of flat portions on the outside of the second sleeve, on which a fork wrench can be fitted, or of radial bores in the second sleeve in which a pin can be engaged for turning the second sleeve.
The device according to the invention uses conveniently ahead screw with a recess defined by surfaces, the cross-section of which defines a regular polygon in which a matching socket wrench can be engaged. At least one of the surfaces defining the recess should enclose with the longitudinal axis of the head screw an outwardly opening small angle different from 0xc2x0. That further development of the invention will be described hereafter with reference to a head screw where the recess has the form of an internal hexagon in which a matching hexagon socket wrench can be engaged. The embodiment using the hexagon is preferred. Other embodiments, especially such using a square or a triangular shape are likewise suited.
A recess of that kind tapers from the outside to the inside. A conventional two-legged bent-off hexagon socket wrench, which is defined by surfaces extending in parallel to the longitudinal axis of its legs, is inserted into the narrowing internal hexagon of the head screw until it is eventually wedged, whereby the head screw is secured against slipping off the hexagon socket wrench unintentionally. Once the thread of the head screw grips in the internal thread of the counter-holder, the socket wrench can be withdrawn from the head screw and can be inserted once more in the hexagonal recess in a different angular position to continue the screwing-in operation.
Another advantageous embodiment uses a head screw whose head is provided with a recess in the form of a conventional internal hexagon defined by axially parallel surfaces. For turning that head screw, a likewise bent-off two-legged hexagon socket wrench, having a shorter and a longer leg, is used. In the case of that wrench, however, the outer hexagon of the shorter and/or the longer leg is defined by surfaces which enclose, with the longitudinal axis of the shorter or the longer leg, a small angle different from 0xc2x0 so that the respective leg tapers towards its tip. In this case, too, the socket wrench is inserted into the recess of the head until it is wedged therein.
In principle, it is sufficient if only one of the surfaces that surround the recess in the head of the screw, only one of the surfaces that define the area of engagement of the socket wrench, encloses with the longitudinal axis of the head screw or with the longitudinal axis of the respective leg of the socket wrench, respectively, an angle different from 0xc2x0. In that case, the best wedging effect is achieved by an angle of 2xc2x0 to 6xc2x0, especially 4xc2x0. The same applies by analogy if more than one surfaces are inclined relative to the respective longitudinal axis at an angle different from 0xc2x0, provided the respective opposite surfaces extend in parallel to the respective longitudinal axis.
Preferably, only two mutually opposite surfaces enclose with the respective longitudinal axis an angle different from 0xc2x0:
In that case, the best wedging effect is achieved if the angle, measured relative to the longitudinal axis, is equal to between 1xc2x0 to 3xc2x0, preferably 2xc2x0, which corresponds to a total opening angle of the two inclined surfaces of between 2xc2x0 to 6xc2x0, preferably 4xc2x0. If more than one pair of opposite surfaces, or all surfaces, are inclined relative to the respective longitudinal axis, the same applies by analogy.